Lithium cell with improved cathode

ABSTRACT

A primary lithium cell having an anode comprising lithium and a cathode comprising electrochemically active material selected from copper vanadates having the formula CuV 2 O 6  or Cu 2 V 2 O 7  or mixtures thereof. The cathode can include a manganese dioxide in admixture with said copper vanadates. The cell exhibits higher capacity and energy output than conventional lithium cells having an anode comprising lithium and cathode comprising manganese dioxide.

FIELD OF THE INVENTION

This invention relates to a lithium electrochemical cell with a cathodecomprising copper vanadates selected from CuV₂O₆ or Cu₂V₂O₇, andmixtures thereof.

BACKGROUND OF THE INVENTION

Electrochemical cells commonly contain a negative electrode (anode) anda positive electrode (cathode), an electrolyte permeable separatortherebetween and an electrolyte in contact with both of the electrodes.Electrolytes can be aqueous-based or non-aqueous organic solvent-basedliquid electrolytes or polymeric electrolytes. There are two basic typesof electrochemical cells, a primary (nonrechargeable) and a secondary(rechargeable) cell. A primary electrochemical cell is discharged toexhaustion only once. A secondary electrochemical cell, however, isrechargeable and thus can be discharged and recharged multiple times.

Primary (non-rechargeable) lithium cells have an anode comprisinglithium and a cathode comprising manganese dioxide, and electrolytecomprising a lithium salt such as lithium trifluoromethane sulfonate(LiCF₃SO₃) dissolved in a mixtures of nonaqueous solvents. These lithiumcells (Li/MnO₂ cells) are commonly in the form of button (coin shaped)cells, prismatic or polyhedral cells (wherein one or more of the housingsurfaces are flat, typically of cuboid, namely, rectangularparallelepiped shape) or cylindrical cells, e.g. ⅔ A cell having about ⅔the height of conventional AA alkaline cells. (The ⅔ A cell has an IECdesignation “CR17335” and has a diameter of about 15 mm and height ofabout 32 mm). The Li/MnO₂ cells have a voltage of about 3.0 volts whichis twice that of conventional Zn/MnO₂ alkaline cells and also have ahigher energy density (watt-hours per cubic centimeter of cell volume)than that of alkaline cells. (Alkaline cells as referenced herein shallbe understood to be conventional commercial alkaline cells having ananode comprising zinc, a cathode comprising manganese dioxide, and anelectrolyte comprising aqueous potassium hydroxide.) Therefore, Li/MnO₂cells can be used in compact electronic equipment, especiallyphotographic cameras, which require operation at higher voltage and athigher power demand than individual alkaline cells.

Primary lithium electrochemical cells typically employ an anode oflithium metal or lithium alloy, preferably a lithium-aluminum alloy; acathode containing an electrochemically active material consisting of atransition metal oxide, preferably manganese dioxide; and an electrolytecontaining a chemically stable lithium salt dissolved in an organicsolvent or a mixture of organic solvents. (The term “anode activematerial” or “cathode active material” as used herein shall beunderstood to mean material in the anode or cathode, respectively, whichundergoes useful electrochemical reaction during cell discharge,contributing to the cell's capacity and voltage.)

The lithium anode is preferably formed from a sheet or foil of lithiummetal or lithium alloy without any substrate or lithium metal depositedor coated on a metallic substrate such as copper or other metals. Alithium primary cell referenced hereinafter as having an anodecomprising “lithium” shall be understood to mean an anode of lithiummetal or a lithium alloy. If a lithium-aluminum alloy is employed, thealuminum is present in a very small amount, typically less than about 1wt % of the alloy. The addition of aluminum primarily serves to improvethe low temperature performance of the lithium anode in lithium primarycells.

Manganese dioxides suitable for use in lithium primary cells includeboth chemically produced manganese dioxide known as “chemical manganesedioxide” or “CMD” and electrochemically produced manganese dioxide knownas “electrolytic manganese dioxide” or “EMD”. CMD can be producedeconomically and in high purity, for example, by the methods describedby Welsh et al. in U.S. Pat. No. 2,956,860. However, CMD typically doesnot exhibit energy or power densities in lithium cells comparable tothose of EMD. Typically, EMD is manufactured commercially by the directelectrolysis of a bath containing manganese sulfate dissolved in asulfuric acid solution. Processes for the manufacture of EMD andrepresentative properties are described in “Batteries”, edited by KarlV. Kordesch, Marcel Dekker, Inc., New York, Vol. 1, 1974, pp.433-488.Manganese dioxide produced by electrodeposition typically is a highpurity, high density, “gamma(γ)-MnO₂ ” phase, which has a complexcrystal structure containing irregular intergrowths of a“ramsdellite”-type MnO₂ phase and a smaller portion of a beta(β)- or“pyrolusite”-type MnO₂ phase as described by dewolfe (ActaCrystallographica, 12, 1959, pp.341-345). The gamma(γ)-MnO₂ structure isdiscussed in more detail by Burns and Burns (e.g., in “StructuralRelationships Between the Manganese (IV) Oxides”, Manganese DioxideSymposium, 1, The Electrochemical Society, Cleveland, 1975, pp.306-327).

Electrochemical manganese dioxide (EMD) is the preferred manganesedioxide for use in primary lithium cells. However, before it can beused, it must be heat-treated to remove residual water. The term“residual water”, as used herein includes surface-adsorbed water,noncrystalline water (i.e., water physisorbed or occluded in pores), aswell as lattice water. Heat-treatment of EMD prior to its use in lithiumcells is well known and has been described by Ikeda et al. (e.g., in“Manganese Dioxide as Cathodes for Lithium Batteries”, Manganese DioxideSymposium, Vol. 1, The Electrochemical Society, Cleveland, 1975, pp.384-401).

EMD suitable for use in primary lithium cells can be heat-treated attemperatures between about 200 and 350° C. as taught by Ikeda et al. inU.S. Pat. No. 4,133,856. This reference also discloses that it ispreferable to heat-treat the EMD in two steps. The first step isperformed at temperatures up to about 250° C. in order to drive offsurface and non-crystalline water. The EMD is heated in a second step toa temperature between about 250 and 350° C. to remove the lattice water.This two-step heat-treatment process improves the discharge performanceof primary lithium cells, primarily because surface, non-crystalline,and lattice water are all removed. An undesirable consequence of thisheat-treatment process is that EMD having the γ-MnO₂-type structure, isgradually converted to EMD having a gamma/beta (γ/β)-MnO₂-typestructure. The term “gamma/beta-MnO₂” as used in the art reflects thefact (as described by Ikeda et al.) that a significant portion of theγ-MnO₂ (specifically, the ramsdellite-type MnO₂ phase) is converted toβ-MnO₂ phase during heat-treatment. At least about 30 percent by weightand typically between about 60 and 90 percent by weight of theramsdellite-type MnO₂ phase is converted to β-MnO₂ during conventionalheat treatment of γ-MnO₂ as taught, for example, in U.S. Pat. No.4,921,689. The resulting γ/β-MnO₂ phase is less electrochemically activethan an EMD in which the γ-MnO₂ phase contains a higher fraction oframsdellite-type MnO₂ relative to β-MnO₂. Thackeray et al. havedisclosed in U.S. Pat. No. 5,658,693 that cathodes containing suchβ-MnO₂-enriched phases exhibit less capacity for lithium uptake duringdischarge in lithium cells.

One consequence of the electrodeposition process used to prepare EMD isthat the formed EMD typically contains “residual surface acidity” fromthe sulfuric acid of the electrolytic bath. This “residual surfaceacidity” must be neutralized, for example, with basic aqueous solution,before the EMD can be used in cathodes for primary lithium cells.Suitable aqueous bases include: sodium hydroxide, ammonium hydroxide(i.e., aqueous ammonia), calcium hydroxide, magnesium hydroxide,potassium hydroxide, lithium hydroxide, and combinations thereof.Typically, commercial EMD is neutralized with a strong base such assodium hydroxide because it is highly effective and economical.

An undesirable consequence of the acid neutralization process is thatalkali metal cations can be introduced into ion-exchangeable sites onthe surface of the EMD particles. For example, when sodium hydroxide isused for acid neutralization, sodium cations can be trapped in thesurface sites. This is especially undesirable for EMD used in cathodesof primary lithium cells because during cell discharge the sodiumcations can be released into the electrolyte, deposit onto the lithiumanode, and degrade the lithium passivating layer. Further, the depositedsodium cations can be reduced to sodium metal, react with the organicelectrolyte solvents, and generate gas, thereby substantially decreasingthe storage life of the cells.

A process for converting commercial grade EMD that has been neutralizedwith sodium hydroxide to the lithium neutralized form is disclosed byCapparella et al. in U.S. Pat. No. 5,698,176 and related Divisional U.S.Pat. No. 5,863,675. The disclosed process includes the steps of: (a)mixing sodium hydroxide neutralized EMD with an aqueous acid solution toexchange the sodium cations with hydrogen ions and produce anintermediate with reduced sodium content; (b) treating the intermediatewith lithium hydroxide or another basic lithium salt to exchange thehydrogen ions with lithium cations; (c) heat-treating the lithiumion-exchanged EMD at a temperature of at least about 350° C. to removeresidual water.

A method for preparing a lithiated manganese dioxide and its use inprimary lithium cells as cathode active material in primary lithiumcells is described in U.S. Pat. No. 6,190,800 (Iltchev) hereinincorporated by reference. The lithiated manganese dioxide recited inthis reference is a heat treated lithiated manganese dioxide producthaving the formula Li_(y)MnO_(2-δ), wherein 0.075≦y≦0.175 and0.01≦δ≦0.06, and a predominantly gamma(γ)-MnO₂-type crystal structure.

Thus, as evidenced by the cited prior art, the methods used to prepareactive cathode materials comprising manganese dioxide or lithiatedmanganese dioxide suitable for cathodes in a primary lithium cellsrequire additional refinement in order to substantially improveperformance of the lithium cells incorporating such active cathodematerials.

SUMMARY OF THE INVENTION

A principal aspect of the invention is directed to a primary(nonrechargeable) lithium cell having an anode comprising lithium, anon-aqueous electrolyte, and a cathode comprising a copper vanadate offormula CuV₂O₆ or Cu₂V₂O₇ as cathode active material. The CuV₂O₆ orCu₂V₂O₇ can be used as cathode active material alone or in any admixturethereof. The CuV₂O₆ can be used in admixture with MnO₂ in any mixturethereof to form the cathode active material for the lithium cell. Itshall be understood that a portion of the MnO₂ in this case can be inthe form of a manganese dioxide such as lithiated manganese dioxide orall of the MnO₂ can be in the form of a lithiated manganese dioxide. TheMnO₂ is preferably heat treated to remove residual water. (The term “amanganese dioxide” shall be understood to include MnO₂ and lithiatedmanganese dioxide.) The lithiated manganese dioxide, for example, asreferenced above and hereinafter can have the formula Li_(y)MnO_(2-δ),wherein 0.075≦y≦0.175 and 0.01≦δ≦0.06 recited in U.S. Pat. No.6,190,800. Alternatively, the Cu₂V₂O₇ if employed as cathode activematerial can be used in admixture with MnO₂ in any mixture thereof toform the cathode active material for the lithium cell. In such case itshall be understood that a portion of the MnO₂ or all of the MnO₂present in the cathode can be in the form of a lithiated manganesedioxide, for example, a lithiated manganese dioxide having the formulaLi_(y)MnO_(2-δ), wherein 0.075≦y≦0.175 and 0.01≦δ≦0.06 as recited inU.S. Pat. No. 6,190,800.

Also, the cathode active material for the lithium cell can comprisemixtures of CuV₂O₆, Cu₂V₂O₇, and MnO₂. All or a portion of the MnO₂ insuch mixtures can be in the form of a lithiated manganese dioxide. Itwill be appreciated that the MnO₂ is desirably heat treated to removeresidual water thereby making it more suitable for use as cathode activematerial in the lithium cell. A conductive carbon, preferably graphitesuch as natural, or synthetic graphite, preferably expanded graphite, isadded to the cathode mixture to improve conductivity.

It has been determined that the primary lithium cell of the inventioncan comprise a conventional anode, namely, a sheet of lithium or lithiumalloy, e.g. lithium-aluminum alloy, preferably, comprising at least 99percent by weight lithium. (An anode comprising “lithium” as referencedherein shall be understood to mean an anode of lithium metal or suchlithium alloy.) The cell may be in the form of a button cell or aspirally wound cell. The electrolyte can be non-aqueous electrolyte,conventionally used in primary lithium cells having a lithium anode andMnO₂ cathode. For example, by way of non-limiting example, theelectrolyte can be a lithium salt, such as lithium perchlorate (LiClO₄)or lithium trifluoromethylsulfonate (LiCF₃SO₃) dissolved in an organicsolvent, for example, dimethoxyethane (DME) or, ethylene carbonate (EC)and propylene carbonate (PC). Gel type polymer electrolytes used inconventional lithium-ion rechargeable cells could also be suitable. Theseparator can be selected from conventional separators for primarylithium cells, for example, the separator can be of microporouspolypropylene.

The copper in CuV₂O₆ or Cu₂V₂O₇ compound has a +2 valence and thevanadium a +5 valence. The Cu⁺² and V⁺⁵ are available for reduction tocopper metal and vanadium (V⁺³) during discharge. On such basis theCuV₂O₆ has a high theoretical specific capacity, namely, 615milliAmp-hour/g and the Cu₂V₂O₇ has a high theoretical capacity of 629milliAmp-hour/g. This is much higher than the theoretical specificcapacity of MnO₂, which is 308 milliAmp-hour/g. Thus, when CuV₂O₆ orCu₂V₂O₇ compounds are used as cathode active material in a primarylithium cell, this results in higher capacity and also higher total“energy output” when compared to same cell having a MnO₂ cathode.

When CuV₂O₆ or Cu₂V₂O₇ are each used alone without any added MnO2, theCuV₂O₆ or Cu₂V₂O₇ desirably comprises between about 60 and 95 percent byweight of the total cathode (electrolyte free basis) . When CuV₂O₆ andCu₂V₂O₇ are used in admixture without any added MnO2, the mixture ofCuV₂O₆ and Cu₂V₂O₇ desirably comprises between about 60 and 95 percentby weight of the total cathode (electrolyte free basis), typicallybetween about 60 and 93 percent by weight of the total cathode(electrolyte free basis).

In cathode mixtures of CuV₂O₆ and MnO2 or mixtures of Cu₂V₂O₇ and MnO2,the CuV₂O₆ or Cu₂V₂O₇ in such mixtures desirably comprises between about1 and 95 percent by weight of the total cathode (electrolyte freebasis), desirably between about 60 and 95 percent by weight of the totalcathode (electrolyte free basis). Typically, the CuV₂O₆ or Cu₂V₂O₇ insuch mixtures comprises between about 60 and 93 percent by weight of thetotal cathode (electrolyte free basis). In such mixture the MnO₂ maytypically comprise between about 10 and 75 percent by weight of thetotal cathode (electrolyte free basis).

If the cathode comprises both CuV₂O₆ and Cu₂V₂O₇ in admixture withmanganese dioxide, then the total amount of CuV₂O₆ and Cu₂V₂O₇ togetheris desirably between about 1 and 95 percent by weight of the totalcathode (electrolyte free basis), desirably between about 60 and 95percent by weight of the total cathode (electrolyte free basis).Typically, the amount of CuV₂O₆ and Cu₂V₂O₇ together in such mixturescomprises between about 60 and 93 percent by weight of the total cathode(electrolyte free basis).

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a cross sectional view of a typical primary lithiumelectrochemical button cell.

DETAILED DESCRIPTION

A primary lithium electrochemical cell can be fabricated in the form ofa button or coin cell 10 as shown in the FIGURE. The primary lithiumcell can also be fabricated in the form of a wound cell, for example, asshown in U.S. Pat. No. 4,707,421, herein incorporated by reference. Inthe button cell shown in the figure, a disk-shaped cylindrical housing30 is formed having an open end 32 and a closed end 38. Housing 30 ispreferably formed from nickel-plated steel, for example. An electricalinsulating member 40, preferably a cylindrical member having a hollowcore, is inserted into housing 30 so that the outside surface ofinsulating member 40 abuts and lines the inside surface of housing 30.Alternatively, the inside surface of housing 30 may be coated with apolymeric material that solidifies into insulator 40 abutting the insidesurface of housing 30. Insulator 40 can be formed from a variety ofthermally stable insulating materials, for example, nylon orpolypropylene. A cathode current collector 15 comprising a metallic gridcan be inserted into the cell so that it abuts the inside surface of theclosed end 38 of the housing 30. The cathode current collector 15 can bewelded onto the inside bottom of the closed end 38 of the housing 30. Anoptional conductive carbon layer 72 comprising a mixture of graphite andpolytetrafluoroethylene (PTFE) binder can be compressed into the cathodecurrent collector 15 and the cathode material 70 coated onto suchconductive layer 72. This may be termed a “staged” cathode construction.

A layer of cathode material 70 of the invention comprising CuV2O6 orCu2V2O7 or any mixture thereof as active cathode material, may thus beinserted over optional conductive layer 72 overlying cathode currentcollector 15. The cathode active material in cathode 70 can be composedentirely of CuV2O6. Alternatively, cathode material 70 can comprisemixtures of CuV2O6 and manganese dioxide or mixtures of CuV2O6 andlithiated manganese dioxide as well as mixtures of CuV2O6, manganesedioxide and lithiated manganese dioxide as the cathode active materialtherein. The lithiated manganese dioxide, for example, can have the formas above referenced in U.S. Pat. No. 6,190,800, herein incorporated byreference.

Alternatively, the cathode active material in cathode 70 can be composedentirely of Cu₂V₂O₇ or mixtures of CuV₂O₆ and Cu₂V₂O₇ with or without anMnO₂ or lithiated MnO₂ added.

In the absence of the conductive layer 72, the layer of cathode material70 is compressed into cathode current collector 15. A separator sheet 60is placed overlying cathode layer 70. Nonaqueous electrolyte is added sothat it fully penetrates through separator sheet 60 and cathode layer70. A layer of anode material 50, typically lithium or lithium alloy isplaced over separator sheet 60. The anode cover 20, formed preferablyfrom nickel-plated steel, is inserted into open end 32 of housing 30 andperipheral edge 35 of housing 30 is crimped over the exposed insulatoredge 42 of insulating member 40. The peripheral edge 35 bites intoinsulator edge 42 closing housing 30 and tightly sealing the cellcontents therein. The anode cover 20 also functions as the negativeterminal of the cell and housing 30 at the closed end 38 functions asthe positive terminal of the cell.

Alternatively, a primary lithium cylindrical cell can be fabricatedcomprising a spirally wound anode and cathode with a separator sheetpositioned therebetween. This electrode configuration for primarylithium cells is well known in the art and an embodiment thereof isdescribed in detail, for example, in U.S. Pat. No. 4,707,421.Compositions for the electrodes, separator, and electrolyte as disclosedin U.S. Pat. No. 4,707,421, herein incorporated by reference, can beused for the primary lithium cells of the present invention except thatthe cathode comprises CuV₂O₆ or Cu₂V₂O₇ or mixtures thereof which caninclude a manganese dioxide added thereto as above referenced.

Synthesis of CuV2O6 and Cu2V2O7

Copper vanadate (CuV₂O₆) was prepared by dry mixing copper oxide (CuO)powder with vanadium pentoxide (V₂O₅) powder in one to one molar ratio.The copper oxide and copper vanadate powders, available from Alfa AesarCo., each had an average particle size of between about 200 and 300micron. Vanadium pentoxide was handled with care within a protectiveenvironment to prevent direct inhalation. The powder mixture was ballmilled in 1 kilogram batches in an electric mixer using zirconia ballsas inert milling medium. The powder was mixed in this manner for up to24 hours to achieve a homogeneous mixture, which was then passed througha sieve to remove the zirconia balls. The filtered mixture was thenplaced in a ceramic container and heated in a conventional oven at atemperature of about 620° C. for about 48 hours in ambient atmosphere.The vanadium pentoxide (V₂O₅) and copper oxide (CuO) powders reacted toform a blue/black powder of single phase crystalline particles havingthe formula CuV₂O₆.

The copper vanadate (CuV₂O₆) product synthesized in the above manner hadthe following properties: The CuV₂O₆ product had a particle sizedistribution wherein 10% by volume of the product fell below 19.4micron; 50% by volume fell below 36.6 micron, and 100% by volume fellbelow 215 micron. The value mean diameter (VMD) which approximates thetrue mean diameter of the CuV₂O₆ particles was 43.6 micron. The CuV₂O₆had a BET surface area of about 0.18 m²/g. The term BET surface area(m²/g) as used herein shall mean the standard measurement of particulatesurface area by gas (nitrogen and/or other gasses) porosimetry as isrecognized in the art. The BET surface area measures the total surfacearea on the exterior of the particle and also that portion of thesurface area defined by the open pores within the particle available forgas adsorption and desorption when applied. BET surface areadeterminations (Brunauer, Emmett and Taylor, method) as reported hereinis carried out in accordance with ASTM Standard Test Method D4820-99.

The CuV₂O₆ product had a low solubility of less than 5 parts per million(PPM) in water at room temperature. The CuV₂O₆ product had a measuredreal density of 4.37 g/cm³ and a calculated theoretical density of 4.396g/cm3. The real density of a solid is the solid sample weight divided byreal volume. The theoretical capacity of the CuV₂O₆ based on reductionof 6 electrons per molecule (Cu⁺² to Cu and V⁺⁵ to V⁺³) is calculated as615 InAh/g.

The out of cell gassing was determined for cathodes comprising CuV₂O₆ inadmixture with lithium trifluoromethane sulfonate (CF₃SO₃Li)electrolyte. The cathode mixture for the gassing test contained 4.5 gCuV₂O₆ and 5 ml electrolyte. The electrolyte comprised a 0.6 M solutionof the (CF₃SO₃Li) in an organic solvent mixture of ethylene carbonate(EC), propylene carbonate (PC), and dimethoxyethane (DME). A comparativecathode mixture comprising manganese dioxide and same electrolyte wasprepared and also tested for out of cell gassing. Each mixture was keptin closed chamber at 70° C. for five days and the amount of gassing wasdetermined by measuring the internal gas pressure within the chamber.The chamber housing the test cathode comprising CuV₂O₆ and sameelectrolyte exhibited an increase in internal pressure of about 20 psig.By contrast the chamber housing the comparative cathode mixture of MnO₂and electrolyte exhibited an increase in internal gas pressure to 45psig.

Copper vanadate (Cu₂V₂O₇) was synthesized in a similar manner usingcopper oxide (CuO) and vanadium pentoxide (V₂O₅) as starting materials.However, the reaction mixture was prepared by mixing the CuO and V₂O₅powders in a stoichiometric ratio of 2 moles CuO to one mole V₂O₅. TheCuO and V₂O₅ powders each had average particle size of between about 200and 300 micron as described above. The mixture was blended with an inertmedia of zirconia balls in an electric mixer for up to 24 hours until ahomogenous mixture was achieved. The powder mixture was separated fromthe inert media and then placed into a ceramic container. The powdermixture in ceramic container was heated in an oven at a finaltemperature of about 700° C. for about 48 hours in ambient atmosphere.At this temperature the CuO and V₂O₅ powders reacted to form acrystalline product having of formula Cu₂V₂O₇.

The cathode 70 for the primary lithium cell of the invention consists ofa cathode active material mixed with suitable polymeric binders, forexample, polytetrafluoroethylene, and conductive agents, for example,carbon black and graphite, to produce a cathode paste or slurry. Thecathode paste can be applied to current collector 15 comprising a highlyporous sintered, felted, or foamed electrically-conductive substrate,for example, a stainless steel grid, an expanded metal foam or a metalfoil. The cathode active material in cathode 70 can comprise the CuV₂O₆or Cu₂V₂O₇ alone or in any mixtures thereof. Manganese dioxide orlithiated manganese dioxide can be added in any percent by weight asadditional cathode active material in admixture with the CuV2O6 orCu2V2O7 cathode active material. (The manganese dioxide, if included asadditional cathode active material is desirably conventionalheat-treated manganese dioxide.) Cathode pieces of the appropriate sizecan be cut from the coated substrate.

The anode 50 comprises anode active material preferably of lithium or alithium alloy. The anode 50 can be a solid sheet of lithium. The anode50 is desirably formed of a continuous sheet of lithium metal (99.8 wt.% pure). Alternatively, anode 50 can be an alloy of lithium and an alloymetal, for example, an alloy of lithium and aluminum. An alloying metal,such as aluminum, can be present at a low concentration, typically lessthan 1 wt. %. Upon cell discharge the lithium in the alloy functionsessentially as pure lithium. Thus, the term “lithium or lithium metal”as used herein and in the claims is intended to include such lithiumalloy. The lithium sheet, forming anode 50 does not require a substrate.The lithium anode 50 is advantageously formed from an extruded sheet oflithium metal having a thickness of desirably between about 0.15 and0.20 mm Alternatively, a much thicker lithium metal anode of about 0.75mm thick could be used for test coin cells, for example, of the typereferenced in the examples.

A separator layer 60 is located between the two electrodes. Theseparator layer typically consists of a porous polymer film or thinsheet that serves as a spacer and prevents electrical contact betweenthe cathode and anode while allowing electrolyte to move freely throughthe pores. Suitable separators can include relatively non-reactivepolymers such as, for example, microporous polypropylene, polyethylene,a polyamide (i.e., a nylon), a polysulfone, or polyvinyl chloride (PVC).The separator has a preferred thickness between about 10 microns and 200microns and a more preferred thickness between about 20 microns and 50microns.

The anode 50, cathode 70 and separator 60 therebetween are containedwithin housing 30. As described hereinabove, the cell can take the formof a coin cell, button cell, cylindrical cell, prismatic cell, laminarcell or other standard cell geometry. The housing 30 is closed toprovide a gas-tight and fluid-tight seal. The housing 30 can be made ofa metal such as nickel, nickel clad or plated steel, stainless steel,aluminum or a plastic material such as PVC, polypropylene, apolysulfone, an acrylic acid-butadiene-styrene terpolymer (ABS), or apolyamide. The housing 30 containing the electrodes and separator can befilled with a suitable liquid or a polymeric nonaqueous electrolyte.

The nonaqueous electrolyte can be any nonaqueous electrolyte orcombination of nonaqueus electrolytes known in the art. Typically,nonaqueous electrolytes suitable for use in a primary lithium/MnO₂ cellcomprise a lithium salt dissolved in an organic solvent or combinationof organic solvents. Typically, the salt is lithium perchlorate (LiClO₄)or lithium trifluoromethylsulfonate (LiCF₃SO₃) . Other suitableelectrolyte salts include: LiPF₆, LiAsF₆, LiBF₄, lithiumbis(trifluoromethylsulfonyl) imide (Li(CF₃SO₂)₂N), and lithium bis(perfluoroethylsulfonyl) imide (Li(CF₃CF₂SO₂)₂N). Suitable organicsolvents include ethylene carbonate(EC), propylene carbonate(PC),butylene carbonate, and the like; dimethylcarbonate (DMC); diethylcarbonate (DEC), ethyl methyl carbonate (EMC), dimethoxyethane (DME);dioxolane; gamma(γ)-butyrolactone; diglyme; and mixtures thereof. Apreferred electrolyte composition consists of a 0.6 M solution oflithium trifluoromethylsulfonate (CF₃SO₃Li; available under thetradename, FC-122, from 3M) in a mixture of dry ethylene carbonate,propylene carbonate, and dimethoxyethane. Once filled with thenonaqueous electrolyte, the housing 30 is sealed to confine thenonaqueous electrolyte and to inhibit the infiltration of moisture andair into the cell.

The following examples illustrate the invention. Test cells wereprepared and balanced so that they were cathode limited, (theoreticalcapacity of lithium divided by theoretical capacity of total cathodeactives above about 1). The cathode theoretical capacity is calculatedusing the following theoretical specific capacities: Li, 3860 mAh/g;MnO₂, 308 mAh/g; CuV₂O₆, 615 mAh/g; and Cu₂V₂O₇, 629 mAh/g.

EXAMPLE 1 Comparative—Lithium Anode/MnO2 Cathode

A button cell 10 is made in accordance with the above description. Thebutton cell 10 was a standard 2430 size having the overall dimensions24.47 mm diameter and 2.46 mm thickness. The anode material 50 was asabove described comprising a sheet of lithium (99.8 wt. % pure). Theanode 50 had a weight of ˜115 mg. In the test cells slight excess Liweight was used in determining the specific capacity of cathode activematerial and also to fill up the void volume inside the cells. Theseparator 60 was of microporous polypropylene membrane of basis weightbetween about 13.5 and 16.5 g/m² and about 0.025 mm thick.

Cathode 70 which was coated onto conductive carbon layer 72 had thefollowing formulation: manganese dioxide (electrolytic manganesedioxide, EMD), 70.0 wt. %, tetrafluoroethylene (Teflon polymer), 3.0 wt.%, conducting carbon additive 27 wt. % (mixtures of Shawinigan carbonblack and particulate graphite such as expanded graphite from TimcalGroup in different ratios). The manganese dioxide was heat treated inconventional manner to remove residual water (non-crystalline water)therefrom before the cathode coating 70 was prepared. The cathode 70 canbe prepared by mixing the above components in a conventional electricblender at room temperature until a homogenous mixture is obtained. Thecathode mixture 70 can be coated on one side of the cathode currentcollector 15. The cathode current collector was a stainless steelexpanded metal foil (EXMET stainless steel foil) having a basis weightof about 0.024 g/cm³. After the anode 50 and cathode 70 is inserted withseparator 60 the housing 30 is filled with the above describedelectrolyte consisting of a 0.6 M solution of lithiumtrifluoromethylsulfonate (CF₃SO₃Li; available under the tradename,FC-122, from 3M) in a mixture of dry ethylene carbonate, propylenecarbonate, and dimethoxyethane. Cell 10 was then sealed as abovedescribed. Cathode Composition, wt. % MnO₂ 70.0 Tetrafluoroethylene 3.0Teflon polymer Particulate graphite 27.0 Total 100.0

Fresh cells 10 were discharged at a constant current of 1 milliAmp and10 milliAmp to a cut off of 1.5 volts. The 1 mA and 10 mA rate in thebutton cell corresponds to a rate of about 248 mA/g and 171 mA/g,respectively, of the manganese dioxide cathode active material. Thecells specific capacity for actives (mAmp-hours/g) and energy output fortotal cathode actives (mWatt-hours/g), (mWatt-hours/cc) is reported inTable 1 for discharge at 1 milliamp and Table 2 for discharge at 10milliamp.

EXAMPLE 2 Lithium Anode/CuV2O6 Cathode

A button cell 10 is made as in Example 1 employing the same size cell,same anode, same electrolyte and components, except that the cathodecompositon was changed to employ CuV₂O₆ as cathode active material.

Cathode 70 has the following formulation: CuV₂O₆, 70 wt. %; particulategraphite (expanded graphite from Timcal Group), 27 wt. %;tetrafluoroethylene (Teflon) binder, 3 wt. %. The cathode 70 can beprepared by mixing the above components in a conventional electricblender at room temperature until a homogenous mixture is obtained. Thecathode mixture 70 can be coated on one side of the cathode currentcollector 15. The cathode current collector was a stainless steelexpanded metal foil (EXMET stainless steel foil) having a basis weightof about 0.024 g/cm³. The cathode composition is summarized as follows:Cathode Composition, wt. % CuV₂O₆ 70.0 Tetrafluoroethylene 3.0 Teflonpolymer Particulate graphite 27.0 Total 100.0

Fresh lithium button cells 10 were prepared having a cathode containing0.04 gram copper vanadate (CuV₂O₆) and were balanced so that they werecathode limited. The cells were discharged at a constant current of 1milliAmp and 10 milliAmp to a cut off of 1.5 volts. The 1 mA and 10 mArate in the button cell corresponds to a rate of about 25 mA/g and 250mA/g, respectively, of the cathode active material. (Also 1 milliAmprate in the above button cell using 0.04 gram CuV₂O₆ corresponds toapproximately a ˜150 milliAmp rate for a ⅔ A cell using about 6 gram ofCuV2O6. The 10 milliAmp rate in the above button cell using 0.04 gramCuV₂O₆ corresponds to approximately a ˜1500 milliAmp rate for a ⅔ A cellusing about 6 gm of CuV₂O₆ actives). The cells specific capacity foractives (mAmp-hours/g) and energy output for total cathode actives(mwatt-hours/g), (mWatt-hours/cc) is reported in Table 1 for dischargeat 1 milliamp and Table 2 for discharge at 10 milliamp.

EXAMPLE 3 Lithium Anode/Cu2V2O7 Cathode

A button cell 10 is made as in Example 1 employing the same size cell,same anode, same electrolyte and components, except that the cathodecomposition was changed to employ Cu₂V₂O₇ as cathode active material.

Cathode 70 has the following formulation: Cu₂V₂O₇, 70 wt. %; particulategraphite (expanded graphite from Timcal Group), 27 wt. %;tetrafluoroethylene (Teflon) binder, 3 wt. %. The cathode 70 can beprepared by mixing the above components in a conventional electricblender at room temperature until a homogenous mixture is obtained. Thecathode mixture 70 can be coated on one side of the cathode currentcollector 15. The cathode current collector was a stainless steelexpanded metal foil (EXMET stainless steel foil) having a basis weightof about 0.024 g/cm³. The cathode composition is summarized as follows:Cathode Composition, wt. % Cu₂V₂O₇ 70.0 Tetrafluoroethylene 3.0 Teflonpolymer Particulate graphite 27.0 Total 100.0

Fresh lithium button cells 10 were prepared having a cathode containing0.04 gram copper vanadate (Cu₂V₂O₇) and were balanced so that they werecathode limited. The cells were discharged at a constant current of 1milliAmp and 10 milliAmp to a cut off of 1.5 volts. The 1 mA and 10 mArate in the button cell corresponds to a rate of about 25 mA/g and 250mA/g, respectively, of the cathode active material. (Also 1 milliAmprate in the above button cell using 0.04 gram Cu₂V₂O7 corresponds toapproximately a ˜150 milliAmp rate for a ⅔ A cell using about 6 gram ofCuV2O6. The 10 milliAmp rate in the above button cell using 0.04 gramCuV₂O₆ corresponds to approximately a ˜1500 milliAmp rate for a ⅔ A cellusing about 6 gm of Cu₂V₂O₆ actives). The cells specific capacity foractives (mAmp-hours/g) and energy output for total cathode actives(mwatt-hours/g), (mWatt-hours/cc) is reported in Table 1 for dischargeat 1 milliamp and Table 2 for discharge at 10 milliamp.

EXAMPLE 4 Lithium Anode/(CuV2O6+MnO₂ Cathode

A button cell 10 is made as in Example 1 employing the same size cell,same anode, same electrolyte and components, except that the cathodecomposition was changed to employ CuV₂O₆ in admixture with MnO₂ ascathode active material.

Cathode 70 has the following formulation: CuV₂O₆, 35 wt. % MnO₂, 35 wt.%; particulate graphite (expanded graphite from Timcal Group), 27 wt. %;tetrafluoroethylene (Teflon) binder, 3 wt. %. The MnO₂ was heat treatedto remove residual water before use in the cathode. The cathode 70 canbe prepared by mixing the above components in a conventional electricblender at room temperature until a homogenous mixture is obtained. Thecathode mixture 70 can be coated on one side of the cathode currentcollector 15. The cathode current collector was a stainless steelexpanded metal foil (EXMET stainless steel foil) having a basis weightof about 0.024 g/cm³. The cathode composition is summarized as follows:Cathode Composition, wt. % CuV₂O₆ 35.0 MnO2 35.0 Tetrafluoroethylene 3.0Teflon polymer Particulate graphite 27.0 Total 100.0

Fresh lithium button cells 10 were prepared having a cathode containing0.1 gram cathode actives (CuV₂O₆+MnO2) and were balanced so that theywere cathode limited. The cells were discharged at a constant current of1 milliAmp and 10 milliAmp to a cut off of 1.5 volts. The 1 mA and 10 mArate in the button cell corresponds to a rate of about 10 mA/g and 100mA/g, respectively, of the cathode active material. (Also 1 milliAmprate in the above button cell using 0.1 gram cathode actives (CuV₂O₆plus MnO₂) corresponds to approximately a ˜60 milliAmp rate for a ⅔ Acell using about 6 gram of same composition cathode actives. The 10milliAmp rate in the above button cell using 0.1 gram cathode actives(CuV₂O₆ plus MnO₂) corresponds to approximately a ˜600 milliAmp rate fora ⅔ A cell using about 6 gm of same composition cathode actives). Thecells specific capacity for actives (mAmp-hours/g) and energy output fortotal cathode actives (mWatt-hours/g), (mWatt-hours/cc) is reported inTable 1 for discharge at 1 milliamp and Table 2 for discharge at 10milliamp.

EXAMPLE 5 Lithium Anode/CuV2O6+Cu2V2O7 Cathode

A button cell 10 is made as in Example 1 employing the same size cell,same anode, same electrolyte and components, except that the cathodecomposition was changed to employ CuV₂O₆ in admixture with Cu₂V₂O₇ ascathode active material.

Cathode 70 has the following formulation: CuV₂O₆, 52.5 wt. %; Cu₂V₂O₇,17.5 wt. %; particulate graphite (expanded graphite from Timcal Group),27 wt. %; tetrafluoroethylene (Teflon) binder, 3 wt. %. The MnO₂ washeat treated to remove residual water before use in the cathode. Thecathode 70 can be prepared by mixing the above components in aconventional electric blender at room temperature until a homogenousmixture is obtained. The cathode mixture 70 can be coated on one side ofthe cathode current collector 15. The cathode current collector was astainless steel expanded metal foil (EXMET stainless steel foil) havinga basis weight of about 0.024 g/cm³. The cathode composition issummarized as follows: Cathode Composition, wt. % CuV₂O₆ 52.5 Cu₂V₂O₇17.5 Tetrafluoroethylene 3.0 Teflon polymer Particulate graphite 27.0Total 100.0

resh lithium button cells 10 were prepared having a cathode containing0.1 gram copper vanadates (CuV₂O₆ plus Cu₂V₂O₇) and were balanced sothat they were cathode limited. The cells were discharged at a constantcurrent of 1 milliAmp and 10 milliAmp to a cut off of 1.5 volts. The 1mA and 10 mA rate in the button cell corresponds to a rate of about 10mA/g and 100 mA/g, respectively, of the cathode active material. (Also 1milliAmp rate in the above button cell using 0.1 gram cathode actives(CuV₂O₆ plus Cu₂V₂O₇) corresponds to approximately a ˜60 milliAmp ratefor a ⅔ A cell using about 6 gram of same composition of cathodeactives. The 10 milliAmp rate in the above button cell using 0.1 gramcathode actives (CuV₂O₆ plus Cu₂V₂O₇) corresponds approximately a ˜600milliAmp rate for a ⅔ A cell using about 6 gm of same composition ofcathode actives). The cells specific capacity for actives (mAmp-hours/g)and energy output for total cathode actives (mWatt-hours/g),(mWatt-hours/cc) is reported in Table 1 for discharge at 1 milliamp andTable 2 for discharge at 10 milliamp. TABLE 1 Fresh Lithium Button CellWith Cathode¹ Comprising CuV₂O₆ or Cu₂V₂O₇ (and mixtures) Discharged at1 mAmp. to 1.5 Volt cut-off at Ambient Temperature Specific EnergyEnergy Capacity Out out Cathode for Total of Total of Total ActivesCathode Cathode Cathode Weight % of Actives Actives Actives, Example²total cathode) (mAh/g) (mWh/g) (mWh/cc) Ex. 1 MnO₂ (70 wt. %) 248 6112345 Comparison Ex. 2 CuV₂O₆ (70 wt. %) 424 1031 4435 Ex. 3 Cu₂V₂O₇ (70wt. %) 388 893 3618 Ex. 4 CuV₂O₆ (35 wt. %); 327 695 3161 MnO₂ (35 wt.%) Ex. 5 CuV₂O₆ (52.5 wt. %); 356 713 3021 Cu₂V₂O₇(17.5 wt. %)Notes:¹The CuV₂O₆ and Cu₂V₂O₇ in the above table was synthesized at about 620°C. and 700° C., respectively, resulting in a single phase product withdesirable microstructure and generally high# particle size distribution. The cathodes comprising CuV₂O₆ or Cu₂V₂O₇and mixtures thereof exhibited very little gassing when the cells weredischarged.²Examples 1, 2 and 3 were based on cells with 0.04 gram of cathodeactives. Examples 4 and 5 were based on cells with 0.1 gram cathodeactives.

TABLE 2 Fresh Lithium Button Cell With Cathode¹ Comprising CuV₂O₆ orCu₂V₂O₇ (and mixtures) Discharged at 10 mAmp. to 1.5 Volt cut-off atAmbient Temperature Specific Energy Energy Capacity Out out Cathode forTotal of Total of Total Actives Cathode Cathode Cathode Weight % ofActives Actives Actives, Example² total cathode) (mAh/g) (mWh/g)(mWh/cc) Ex. 1 MnO₂ (70 wt. %) 171 380 1823 Comparison Ex. 2 CuV₂O₆ (70wt. %) 385 870 3742 Ex. 3 Cu₂V₂O₇ (70 wt. %) 358 729 2952 Ex. 4 CuV₂O₆(35 wt. %); 248 545 2485 MnO₂ (35 wt. %) Ex. 5 CuV₂O₆ (52.5 wt. %); 385859 3652 Cu₂V₂O₇(17.5 wt. %)Notes:¹The CuV₂O₆ and Cu₂V₂O₇ in the above table was synthesized at about 620°C. and 700° C., respectively, resulting in a single phase product withdesirable microstructure and generally high# particle size distribution. The cathodes comprising CuV₂O₆ or Cu₂V₂O₇and mixtures thereof exhibited very little gassing when the cells weredischarged.²Examples 1, 2 and 3 were based on cells with 0.04 gram of cathodeactives. Examples 4 and 5 were based on cells with 0.1 gram cathodeactives.

The test lithium cells employing cathodes comprising CuV₂O₆ or Cu₂V₂O₇or mixtures thereof show generally much higher actual specific capacity(mAmp-hrs/g of total cathode actives) and higher energy output (mwatt-hrper gram or mwatt-hr per cubic centimeter of total cathode actives) thanthe comparative lithium cells with only MnO₂ actives. This was generallytrue at both discharge rates employed 1 mAmp (Table 1) or 10 mAmp rate(Table 2) and thus reflects the attractiveness of the CuV₂O₆ and Cu₂V₂O₇vanadates as cathode active material for primary lithium cells.

Although the present invention has been described with reference tospecific embodiments, it will be appreciated that variations within theconcept of the invention are possible. Thus, the invention is notintended to be limited to the specific embodiments, but rather isdefined by the claims and equivalents thereof.

1. An electrochemical cell comprising a housing, a positive and anegative terminal, an anode comprising lithium, a cathode comprising acathode active material selected from the group of vanadate compoundsconsisting of CuV₂O₆ and Cu₂V₂O₇ and any mixture thereof.
 2. The cell ofclaim 1 wherein said cell is nonrechargeable.
 3. The cell of claim 1wherein said cathode active material selected from the group of vanadatecompounds consisting of CuV₂O₆ and Cu2V2O7 and any mixtures thereof,comprises between about 1 and 95 percent by weight of the cathode(electrolyte free basis).
 4. The cell of claim 1 wherein said cathodeactive material further comprises a manganese dioxide.
 5. The cell ofclaim 1 wherein said cathode further comprises manganese dioxide heattreated to remove water therefrom.
 6. The cell of claim 1 wherein saidcathode further comprises a lithiated manganese dioxide.
 7. The cell ofclaim 1 wherein said cathode further comprises a conductive carboncomprising graphite.
 8. An electrochemical cell comprising a housing, apositive and a negative terminal, an anode comprising lithium, a cathodecomprising CuV₂O₆, and a nonaqueous electrolyte.
 9. The cell of claim 8wherein the cell is nonrechargeable.
 10. The cell of claim 8 whereinsaid cathode further comprises a manganese dioxide.
 11. The cell ofclaim 8 wherein said cathode further comprises a lithiated manganesedioxide.
 12. The cell of claim 8 wherein the CuV₂O₆ comprises betweenabout 1 and 95 percent by weight of the cathode (electrolyte freebasis).
 13. The cell of claim 8 wherein the CuV₂O₆ comprises betweenabout 60 and 95 percent by weight of the cathode (electrolyte freebasis).
 14. The cell of claim 8 wherein said cathode further comprisesmanganese dioxide heat treated to remove water therefrom.
 15. The cellof claim 8 wherein said cathode further comprises a lithiated manganesedioxide.
 16. The cell of claim 8 wherein said cathode further comprisesa conductive carbon comprising graphite.
 17. An electrochemical cellcomprising a housing, a positive and a negative terminal, an anodecomprising lithium, a cathode comprising Cu₂V₂O₇, and a nonaqueouselectrolyte.
 18. The cell of claim 17 wherein said cell isnonrechargeable.
 19. The cell of claim 17 wherein said cathode furthercomprises a manganese dioxide.
 20. The cell of claim 17 wherein theCu₂V₂O₇ comprises between about 1 and 95 percent by weight of thecathode (electrolyte free basis).
 21. The cell of claim 17 wherein theCu₂V₂O₇ comprises between about 60 and 95 percent by weight of thecathode (electrolyte free basis).
 22. The cell of claim 17 wherein saidcathode further comprises manganese dioxide heat treated to remove watertherefrom.
 23. The cell of claim 17 wherein said cathode furthercomprises a lithiated manganese dioxide.
 24. The cell of claim 17wherein said cathode further comprises a conductive carbon comprisinggraphite.